The present invention relates to the field of optical and magneto-optical recording. More particularly, it relates to an improved optical tape recording media in which the adverse effects of dust and other contaminating particles on the media surface are mitigated by an integral transparent film which, during the recording and playback of information on the media, operates to displace such particles from the media surface and thereby render them substantially transparent to the recording/playback beam.
In the optical recording/playback process, bits of binary data are recorded in an optical recording layer as a track of optically detectable micron-sized pits or spots. The recording of such pits and spots is commonly effected by scanning the recording layer with a focused beam of radiation (e.g., that produced by a laser) while intensity-modulating the beam with the binary information. Recovery of the recorded information is achieved by scanning the recording layer with a sharply focused beam of radiation (e.g., produced by a laser) and monitoring the beam for transmission or reflection variations caused by the irradiated pits or spots.
In the magneto-optic recording process, a series of data bits are recorded in a magnetic recording layer as a track of micron-sized, vertically oriented magnetic domains. During recording, the up/down orientation of these domains is changed by scanning the magnetic layer with an intensity-modulated laser beam while subjecting the layer to a magnetic field in a direction perpendicular to the magnetic layer. The beam intensity, at high power, is sufficient to heat the recording layer to a temperature above its Curie point. Detection of the up/down orientation of the previously recorded magnetic domains is detected by scanning the data track with a plain-polarized beam of radiation and monitoring the beam for shifts in the plane of polarization, as occasioned by the Kerr or Faraday effects.
Owing to the relatively minute size of the recorded data on optical and magneto-optical recording elements, it is easy to appreciate that the presence of contamination particles (e.g., dust) on the recording media surface can wreak havoc on the data recording and playback processes. A single dust particle can obliterate many of the recorded pits, spots or domains, rendering the information they represent non-recoverable. Where the recording element is in the form of a disk, the particle contamination problem has been solved by recording and playing back information through a relatively thick (e.g., greater than 500 microns) transparent layer. Such layer usually takes the form of a plastic or glass substrate which supports the recording layer, as disclosed, for example, in U.S. Pat. No. 4,600,682 to F. W. Spong et al. Alternatively, recording and playback are effected through a thin transparent film or membrane which is maintained at a spaced position above the recording layer. Such an approach is disclosed, for example, in the commonly assigned U.S. Pat. No. 4,365,258 to F. F. Geyer et al. Owing to the spacing between the transparent membrane and the recording layer or, in the case of a contiguous transparent layer, the thickness of such layer, dust particles resting on the exposed surfaces of these transparent members are sufficiently spaced from the recording layer (i.e., the intended plane of focus of the read/write beam) as to prevent such particles from obscuring a significant portion of the focused beam. By this arrangement, contamination particles are not "seen" by the read/write optical system.
While the thick transparent substrate and spaced thin transparent membrane approaches to the contamination problem work well when the recording element is in the form of a disk, it may be appreciated that these solutions are disadvantageous when applied to a recording medium in the form of an elongated web or tape. Adding a 500 micron thick dust-defocusing layer to an optical tape would so increase the thickness of the tape as to severely lomit the recording capacity of a spool or reel of practical diameter.